The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
With the development of mobile communications, radio frequency power amplifiers are widely used in wireless access systems and microwave systems for signals amplifying, and become an important part of the systems. In a Code Division Multiple Access (CDMA) wireless access multi-carrier system, there is only one power amplifier in each sector. If the power amplifier of a sector goes wrong, the connection to the mobile terminals of the sector will fail. Therefore, the CDMA wireless access multi-carrier system puts a great emphasis upon the stability and reliability of the power amplifiers.
Power amplifiers may go wrong easily because of the high-current and high-voltage working conditions and the poor thermal environment. It is necessary to develop standby techniques for power amplifiers so as to improve the stability. The so-called standby refers to: there are two same power amplifiers in the system; in normal state, one of the two power amplifiers is a working power amplifier and the other is a standby power amplifier; when the working power amplifier goes wrong, the standby power amplifier will automatically switch to the working state to take on the operation of the faulted one without a power cut. Besides, a concurring technology is proposed to increase the output power of a power amplifier system, wherein two same power amplifiers in a parallel connection are inputted with the same signals, perform the same operations, and output the same signals, so as to increase the processing capability and output power of the power amplifier system.
A standby and concurring solution of the power amplifier according to the prior art is shown in FIG. 1. According to FIG. 1, the system in the prior art includes a pre-hybrid matrix, a power amplifier matrix, a post-hybrid matrix, two matching resistors R and antennae S1, S2 and S3. The pre-hybrid matrix and the post-hybrid matrix both include four 3 dB electric bridges, respectively, with the pre-hybrid matrix providing a function of dividing signals and the post-hybrid matrix providing a function of combining signals. The power amplifier matrix includes four power amplifiers PA1, PA2, PA3, and PA4, each of which jointly amplifies the signals of the three sectors inputted from the inputs IN1, IN2, IN3 respectively. The transmission lines A1, A2, A3, A4 in FIG. 1 have the same length, so do transmission lines B1, B2, B3, B4, transmission lines C1, C2, C3, C4, and transmission lines D1, D2, D3, D4.
The input signal from IN1 is divided into 4 equal-amplitude signals after passing through the pre-hybrid matrix and then goes to the inputs of the four power amplifiers. Then the four signals are amplified by the power amplifier matrices respectively, combined to one signal by the post-hybrid matrix, and sent to the antenna S1 of sector 1. Depending on the phase superposition of the multiple signals, in an ideal situation, the input signal from IN1, after being divided, amplified and combined, will neither be outputted at the ports of antennae S2 and S3, nor appear on the matching resistor.
Likewise, the input signal from IN2 is outputted to the antenna S2 rather than S1, S3 or the matching resistor R after being divided by the pre-hybrid matrix, amplified by the power amplifier matrix and combined by the post-hybrid matrix; the input signal from IN3 is outputted to the antenna S3 rather than S1, S2 or the matching resistor R after being divided by the pre-hybrid matrix, amplified by the power amplifier matrix and combined by the post-hybrid matrix.
When any one of the power amplifiers in FIG. 1 goes wrong, the three remaining power amplifiers still work normally. The input signals from IN1, IN2, and IN3 can go to the antenna S1, S2, and S3, respectively, after being amplified by the system. Thus the mobile terminals of all the three sectors can access the system and it will not happen that no terminal in one sector is able to access the system.
While being combined by the post-hybrid matrix, the hybrid signal divided by the pre-hybrid matrix will be counteracted from the signals of other sectors depending on the differences in amplitude and phase among the signals, therefore, the requirement on the amplitude and phase of the signals is very strict in the system. If the amplitude relationship and the phase relationship among the signals can not meet the requirement, the signals will not be fully counteracted, thus leading to a cross-interference and a poorer isolation between the sectors. Such is a fatal defect of a power amplifier system.
The following factors will have an impact on the amplitude relationship and the phase relationship among the signals while the signals are divided and combined:
1. Factors in design or technology may make the coupling of the 3 dB electric bridge coupler not be the ideal 3 dB. Even an ideal 3 dB electric bridge coupler can meet the requirement of phase and amplitude simultaneously only at the center frequency, and it is theoretically impossible to simultaneously meet the requirements on amplitude and phase differences at a frequency departing from the center frequency.
2. If the four transmission lines A1, A2, A3 and A4 in the pre-hybrid matrix have different lengths, or the transmission lines B1, B2, B3 and B4 connecting the pre-hybrid matrix and the power amplifier matrix have different lengths, or the transmission lines C1, C2, C3, C4 connecting the power amplifier matrix and the post-hybrid matrix have different lengths, or the transmission lines D1, D2, D3, D4 in the post-hybrid matrix have different lengths, there will be an additional phase difference.
3. The dispersion characteristic mainly resulted from the gain and phase differences among the power amplifiers PA1, PA2, PA3, and PA4 calls for a strict matching among these power amplifiers. A typical requirement on gain difference is less than 0.5 dB while the requirement on phase difference is usually less than 10°.
All the above factors can lead to a poorer isolation between the sectors. With the ordinary technology, it is very difficult to achieve the sector isolation of 25 dB while the performance of 25 dB is unable to meet the protocol requirement of CDMA systems, as well as the requirement on the adjacent frequency interference in the case of special sector configurations. In other words, the requirement on signals isolation between adjacent sectors will not be met with the solution in the prior art.
In commercial applications of the solution according to the prior art, it is necessary to find another power amplifier having exactly the same characteristics of gain and phase as the replaced amplifier when a power amplifier should be replaced, which is very difficult.